Application Of Cavity Ring-down Spectroscopy Research Articles

Application of cavity ring-down spectroscopy and a novel near surface Gaussian plume estimation approach to inverse model landfill methane emissions

Fugitive methane emissions from municipal solid waste landfills impact global climate change and reliable emissions quantification is of increasing importance. Ground-based cavity ring-down spectrometer (CRDS) measurements were used to determine methane concentrations and isotopic compositions of carbon in CH4. Then, CH4 oxidation through various cover materials was assessed using the Keeling plot method. A novel inverse modeling approach using Gaussian dispersion analysis, termed near-surface Gaussian plume estimation (NSGPE), was developed to predict whole-site landfill methane emissions. The concentration data obtained around the landfill perimeter with the mobile ground-based CRDS were used. Methane concentration data were integrated to parameterize discretized point source emissions from a Gaussian dispersion model. Post-processing algorithms were applied to refine modeling predictions to account for the influence of topographical and meteorological conditions on methane transport. Results indicate spatially resolved and consistent emissions estimates among multiple optimization simulations, with refinements increasing the resolution and spatial trends of emissions. Post-processing algorithms resolve consistent overestimation of emissions commonly observed using conventional Gaussian dispersion models.•Ground-based CRDS used to obtain methane concentration and oxidation data.•Novel inverse Gaussian dispersion modeling approach developed to predict methane emissions from landfills accounting for site-specific topography and meteorology.•Post-processing algorithms refine emissions estimates.

Cavity ring-down spectroscopy and its applications to environmental, chemical and biomedical systems

In recent times, the need for high-sensitive detection has grown drastically as more and more applications of molecular sensing are being explored. Cavity ring-down spectroscopy (CRDS) is one of the new age and robust techniques which has revolutionized the field of molecular detection, particularly gas-phase analysis. In this short review, we have first provided a brief introduction to the working principles and system requirements of CRDS. Subsequently, we have described the various applications of CRDS in detail, including environmental monitoring, biomedical analysis specifically human breath analysis and reaction chemistry. We have also focused on the importance of isotope analysis and their accurate measurements using CRDS and its variants. Furthermore, we described the use of CRDS in the condensed phase through evanescent wave (EW) coupled CRDS and discussed its applications in the investigation of interfacial kinetics, thin-film and biological detection. We also outlined certain variants of CRDS to give a glimpse of the different techniques which have emerged with CRDS. Hence, in this mini-review, we aimed to illustrate the use of the CRDS technique in various interdisciplinary fields. SYNOPSIS The review provides an overview of the cavity ring-down spectroscopy (CRDS) technique and its variants. The applications of CRDS in environmental monitoring, biomedical diagnostics, reaction chemistry and isotope analysis for both the gas phase and the condensed phase molecules have been discussed.

Gaseous Oxygen Detection Using Hollow-Core Fiber-Based Linear Cavity Ring-Down Spectroscopy

We demonstrate a method for the calibration-free and quantitative analysis of small volumes of gaseous samples. A 10 m hollow-core photonic bandgap fiber is used as the sample cell (volume = 0.44 $\mu$ L) and is placed inside a linear resonator setup. The application of cavity ring-down spectroscopy and in consideration of rather small coupling losses, this leads to an increased effective optical path length of up to 70 m. This implies a volume per optical interaction path length of 6.3 nL $\cdot$ m $^{-1}$ . We used tunable diode laser spectroscopy at 760 nm and scanned the absorption for oxygen sensing. The optical loss due to sample absorption is obtained by measuring the ring-down time of light propagating inside the cavity. The resultant absorption coefficient shows a discrepancy of only 5.1% comparing to the HITRAN database. This approach is applicable for sensitive measurements if only submicroliter sample volumes are available.

Measurement of δ18O and δ2H values of fluid inclusion water in speleothems using cavity ring‐down spectroscopy compared with isotope ratio mass spectrometry

The hydrogen and oxygen isotopic analyses (δ(2)H and δ(18)O values) of water trapped within speleothem carbonate (fluid inclusions) have traditionally been conducted utilizing dual-inlet isotope ratio mass spectrometry (IRMS) or continuous-flow (CF)-IRMS methods. The application of cavity ring-down spectroscopy (CRDS) to the δ(2)H and δ(18)O analysis of water in fluid inclusions has been investigated at the University of Miami as an alternative method to CF-IRMS. An extraction line was developed to recover water from the fluid inclusions consisting of a crusher, sample injection port and an expansion volume (either 100 or 50 cm(3)) directly connected to the CRDS instrument. Tests were conducted to determine the reproducibility of standard water injections and crushes. In order to compare results with conventional analytical methods, samples were analyzed both at the University of Miami (CRDS method) and at the Vrije Universiteit Amsterdam (CF-IRMS method). The analytical reproducibility of speleothem samples crushed on the Miami Device demonstrates an average external standard deviation of 0.5 and 2.0 ‰ for δ(18)O and δ(2)H values, respectively. Sample data are shown to fall near the global meteoric water line, supporting the validity of the method. Three different samples were analyzed at Vrije Universiteit Amsterdam and the University of Miami in order to compare the performance of each laboratory. The average offset between the two laboratories is 0.7 ‰ for δ(18)O and 2.5 ‰ for δ(2)H. The advantage of CRDS is that the system is a low-cost alternative to CF-IRMS for fluid inclusion isotope analysis. The CRDS method demonstrates acceptable precision and good agreement with results from the CF-IRMS method. These are promising results for the future application of CRDS to fluid inclusion isotope analysis.

Cavity ring down spectroscopy: detection of trace amounts of substance

AbstractWe describe several applications of cavity ring-down spectroscopy (CRDS) for trace matter detection. NO2 sensor was constructed in our team using this technique and blue-violet lasers (395–440 nm). Its sensitivity is better than single ppb. CRDS at 627 nm was used for detection of NO3. Successful monitoring of N2O in air requires high precision mid-infrared spectroscopy. These sensors might be used for atmospheric purity monitoring as well as for explosives detection. Here, the spectroscopy on sharp vibronic molecular resonances is performed. Therefore the single mode lasers which can be tuned to selected molecular lines are used. Similarly, the spectroscopy at 936 nm was used for sensitive water vapour detection. The opportunity of construction of H2O sensor reaching the sensitivity about 10 ppb is also discussed.

Application of cavity ring-down spectroscopy to the Boltzmann constant determination

The Boltzmann constant can be optically determined by measuring the Doppler width of an absorption line of molecules at gas phase. We propose to apply a near infrared cavity ring-down (CRD) spectrometer for this purpose. The superior sensitivity of CRD spectroscopy and the good performance of the near-ir lasers can provide ppm (part-per-million) accuracy which will be competitive to present most accurate result obtained from the speed of sound in argon measurement. The possible influence to the uncertainty of the determined Doppler width from different causes are investigated, which includes the signal-to-noise level, laser frequency stability, detecting nonlinearity, and pressure broadening effect. The analysis shows that the CRD spectroscopy has some remarkable advantages over the direct absorption method proposed before. The design of the experimental setup is presented and the measurement of C2H2 line near 0.8 μm at room temperature has been carried out as a test of the instrument.

High-Resolution Spectroscopic Measurements of InGaAs/GaAs Self-Assembled Quantum Dots

We report development of two absorption-based spectroscopic methods that have been adapted from atomic physics techniques to elucidate the basic physical properties of InGaAs/GaAs self-assembled quantum dots(SAQDs). Absorptive spectroscopic measurements allow the examination of the SAQDs optical transitions free from carrier relaxation effects. In addition, we employ these techniques to study SAQDs' optical transition with a level of spectral resolution not available using ultra-fast techniques. The first of the two approaches we discuss is cavity ring-down spectroscopy (CRDS), which permits an absolute measurement of absorption. We report on initial application of CRDS to SAQDs and present an assessment based on these measurements for single SAQD spectroscopy using this technique. The second method, spectral hole burning, is applied to SAQDs in a semiconductor ridge waveguide and permits the homogeneous linewidth of the SAQDs to be separated from the broad inhomogeneous spectrum.

Applications of cavity ring-down spectroscopy to high precision isotope ratio measurement of 13C/12C in carbon dioxide

Recent measurements of carbon isotopes in carbon dioxide using near-infrared, diode-laser-based cavity ring-down spectroscopy (CRDS) are presented. The CRDS system achieved good precision, often better than 0.2‰, for 4% CO2 concentrations, and also achieved 0.15–0.25‰ precision in a 78 min measurement time with cryotrap-based pre-concentration of ambient CO2 concentrations (360 ppmv). These results were obtained with a CRDS system possessing a data rate of 40 ring-downs per second and a loss measurement of 4.0 × 10−11 cm−1 Hz−1/2. Subsequently, the measurement time has been reduced to under 10 min. This standard of performance would enable a variety of high concentration (3–10%) isotopic measurements, such as medical human breath analysis or animal breath experiments. The extension of this ring-down to the 2 μm region would enable isotopic analysis at ambient concentrations, which, combined with the small size, robust design, and potential for frequent measurements at a remote site, make CRDS technology attractive for remote atmospheric measurement applications.

Ultra-sensitive ethylene post-harvest monitor based on cavity ring-down spectroscopy

We describe the application of cavity ring-down spectroscopy (CRDS) to the detection of trace levels of ethylene in ambient air in a cold storage room of a fruit packing facility over a several month period. We compare these results with those obtained using gas chromatography (GC), the current gold standard for trace ethylene measurements in post-harvest applications. The CRDS instrument provided real-time feedback to the facility, to optimize the types of fruit stored together, and the amount of room ventilation needed to maintain sub-10 ppb ethylene levels for kiwi fruit storage. Our CRDS instrument achieved a detection limit of two parts-per-billion volume (ppbv) in 4.4 minutes of measurement time.

Solving chemical problems of environmental importance using cavity ring-down spectroscopy.

Cavity ring-down (CRD) is a sensitive variant of traditional absorption spectroscopy that has found increasing use in a number of chemical measurement applications. This review focuses on applications of cavity ring-down spectroscopy that will be of interest to environmental chemists and analytical chemists working on environmental problems. The applications are classified into direct monitoring approaches, indirect analysis methods and ancillary studies and a differentiation is made between field-tested instruments and proof of principle studies.

Cavity ring-down spectroscopy for atmospheric trace gas detection: application to the nitrate radical (NO 3 )

Cavity ring-down spectroscopy is a relatively new and quite sensitive technique for the measurement of gas-phase optical extinction. It holds the potential for simple, direct and sensitive measurement of the concentrations of a variety of trace gases in the atmosphere. For example, detection of the nitrate radical, NO3, and its companion, dinitrogen pentoxide, N2O5, has been demonstrated with a sensitivity of 0.25 pptv (1σ). This paper considers several of the requirements for the application of cavity ring-down spectroscopy to concentration measurements of trace gases in ambient air. These include detection sensitivity, measurement of an accurate zero in the presence of competing absorbers, cavity stability and mirror cleanliness, laser line-width effects, saturation effects, Rayleigh scattering, the influence of atmospheric aerosols and sampling issues for reactive species. Examples drawn from our work on NO3 and N2O5 detection in the field illustrate these considerations.

Simultaneous in situ detection of atmospheric NO3 and N2O5 via cavity ring-down spectroscopy

This article describes the application of cavity ring-down spectroscopy (CaRDS) to the simultaneous concentration measurement of nitrate radical, NO3, and dinitrogen pentoxide, N2O5, in the ambient atmosphere. The sensitivity for detection of both NO3 and N2O5 is 0.5 pptv (2σ) for a 5 s integration, comparable to or better than previous measurements of NO3 (e.g., via DOAS), but with significantly better time resolution. Furthermore, direct measurement of N2O5 represent a previously unavailable capability. Concentrations of both species are measured simultaneously in two separate flow systems and optical cavities pumped by the same pulsed dye laser at 662 nm. One of the flow systems remains at ambient temperature for detection of NO3, while the other is heated to 80 °C to induce thermal decomposition of N2O5 providing a measurement of the sum of the NO3 and N2O5 concentrations. This article outlines a series of laboratory and field tests of the instrument’s performance. Important considerations include signal acquisition, zero measurements, aerosol interference, flow system losses, and the conversion efficiency for N2O5 thermolysis to NO3. We describe the limitations of this method and show how they can be quantified and accounted for in field measurements.

Investigation of kinetics of CH-radicals decay by cavity ring-down spectroscopy

We describe application of cavity ring-down spectroscopy (CRDS) for monitoring of CH-radicals produced by pulsed electric discharge in methane. The method provides opportunity to follow changes of concentration of the reaction product within a few microseconds.

In‐situ measurement of atmospheric NO3 and N2O5 via cavity ring‐down spectroscopy

We report the application of cavity ring‐down spectroscopy (CaRDS), a high‐sensitivity absorption technique, to the in‐situ detection of both NO3 and N2O5 in ambient air. The detection limit for NO3, measuring absorption in its strong, 662‐nm band, is 0.3 pptv at STP (50 s integration time). Heating the air flow through the inlet thermally dissociates N2O5 to yield NO3, whose detection gives the ambient concentration of N2O5. The instrument was successfully field tested in March–April, 2001 at a site in the tropospheric boundary layer in Boulder, Colorado. This study is the first fast‐response (5s‐1 min), in‐situ detection of NO3. It is also the first in‐situ detection of N2O5 and the first observation of this species in the troposphere. Both NO3 and N2O5 showed considerable temporal variability, highlighting the need for a fast‐response instrument.

Kinetic Studies of the Reactions of IO Radicals Determined by Cavity Ring-Down Spectroscopy

We demonstrate the application of cavity ring-down spectroscopy (CRDS) to the measurement of concentrations of IO radical and of reaction rate coefficients for the reaction systems, IO + IO and IO + NO, using the source reaction, O(3P) + CF3I. By monitoring IO radicals, we obtain the 295 K rate coefficients, k(O + CF3I → IO + CF3) = (5.8 ± 1.5) × 10-12 cm3 molec-1 s-1; k(IO + IO) = (1.0 ± 0.3) × 10-10 cm3 molec-1 s-1, and k(IO + NO) = (1.9 ± 0.5) × 10-11 cm3 molec-1 s-1 at the pressures of 1250 Pa (9.4 Torr) and 4000 Pa (30.1 Torr). For the IO A 2Π3/2 − X 2Π3/2 (2, 0) bandhead at 445.04 nm we have determined an absorption cross-section, σ = (7.3 ± 0.7) × 10-17 cm2. Error limits indicate the confidence of two standard deviations and propagate the uncertainty in the absorption cross-section.